Momentum-dependent annihilation rate for positrons in metals

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Abstract
Results are presented of a calculation for the partial annihilation rate of a thermalized positron with electrons in a metal as a function of the initial electron momentum. The method used has previously been successfully applied to the calculation of total annihilation rates. Recent work has shown that the agreement with experimental total rates is even better than was originally claimed. In this method the positron-electron wave function is calculated self-consistently using an effective interaction which includes strong interaction effects from no more than one highly correlated screening electron at any instant of time. Within the formalism self-energy insertions must be retained. The partial rates are more sensitive to these insertions than are the total rates. The calculated partial annihilation rates in the electron gas at metallic densities are all monotonically increasing functions of the initial electron momentum up to the Fermi surface. For lithium the partial rate is in good agreement with experimental data.